the others are intermediate ; fig. 3 shewing long radii 
with large tubercles ; and figures 4 and 5 irregular radii 
with undefined tubercles. 
AMMONITES tuberailatus. 
TAB. CCC X.—Figs. 1, 2, and 3. 
Spec. Char. Depressed, radiated ; volutions gib- 
bose, half concealed, front rather flat; radii 
arising in threes from large round tubercles 
and uniting in pairs to form large compressed 
tubercles upon each edge of the front; aper- 
ture suborbicular. 
The sides of the whorls are very convex especially in 
young shells which have the aperture transverse, the 
round tubercles are placed near the middle of the side of 
the whorl ; the radii after uniting to form the flat tuber- 
' cles upon each edge of the front, bend forward and 
continue over it as far as the siphuncle, which they meet 
at an acute angle ; the length of the mouth is about two- 
fifths the diameter of the last whorl, its width variable 
with age. 
AMMONITES proboscideus. 
TAB. CCC X.—Figs. 4 and 5. 
Spec. Char. Depressed, tuberculated ; volutions ven- 
tricose, partly concealed ; front concave ; tubercles 
upon the sides of the last whorl and both edges of 
the front, subcylindrical ; aperture orbicular, 
var. a, tubercles connected by very irregular and short 
radii. — var. /3, destitute of radii. 
T'iir orbicular aperture, and elongated nearly cylindrical 
tubercles, distinguish this species : there arc about eight sets 
of tubercles only upon each whorl, in the preceding species 
there are 12 or more : the front is broad but not well defined, 
and the siphuncle very large. The aperture is about one- 
third the diameter of the shell wide. 
The four species of Ammonites above described are all from 
a stratum of Marie below the Chalk at Folkstone ; they are also 
found in a similar stratum at Cambridge and other places. It 
is difficult to divide the species, as there appears to be a regular 
series from that without tubercles (A. dentatus) to one with 
large flat tubercles upon the margin (A. auritus, M. C. t. 134,) 
and to another with cylindrical tubercles at each end of the 
rays, (A. proboscideus) ; the extremes are, however, so dis- 
tinct, that it is difficult to refuse them the rank of species. 
They are all splendidly pearly shells, but are very apt to be 
destroyed by the decomposition of the Pyrites, with which they 
are commonly more or less completely filled; those parts that 
are not pyritous are in the Folkstone specimens filied with black 
indurated* Marie. 
